Kohzoh Ohtsu

ELECTRICAL ACTIVITIES OF THE ANTHOMEDUSAN, SPIROCODON SALTATRIX (TILESIUS)

1. Electrical activities occurring spontaneously and in response to electrical or photic stimulation were recorded from nervous, muscular and non-nervous tissues of Spirocodon saltatrix.2. Two types of quick pulses, nMPs and PSPs, were recorded from the nerve ring. nMPs originated in the outer nerve ring and PSPs, in both the outer and the inner nerve rings. The PSPs appeared to trigger swimming contractions because they always preceded the muscle contraction pulses of the bell (SSPs) and the velum(VSPs).3. Composite pulses with quick and slow phases (QSCPs) and slow monophasic pulses (SMPs) were recorded on the subtentacular region and the tentacles, respectively. The QSCPs had an intimate relationship with nMPs and their quick components appeared to be of nervous origin as were nMPs and PSPs. The SMPs seemed to be myonal or epithelial events and their conduction was restricted to each radial streak.4. Contraction pulses of the velum (VSPs) and the subumbrellar muscle (SSPs) consisted of ...

Ultrastructural Studies of Calcium Location during the “Catch” Contraction of Clam Smooth Adductor Muscle Cells

Abstract Contraction of molluscan adductors has been classified into three states; 1) resting state, 2) contracted state, 3) prolonged “catch” state. Among these, the “catch” state is considered a peculiar state, which requires little expenditure of energy, but in which contraction can be maintained for long periods. It is not yet known whether “catch” muscle contraction is regulated by Ca, or where Ca translocates during resting state through “catch” state, if the muscle contraction is regulated by Ca. We attempted to observe Ca translocation in muscle cells during contraction by the K-pyroantimonate method. We fixed “catch” muscle cells for electron microscopy with fixative including K-pyroantimonate, and observed where electron-dense precipitates, in which Ca is concentrated, were located in the muscle cells in the three states of contraction. At the resting state, precipitate was located at cell peripheries, in positions such as at the inner surface of cell membranes and in sarcoplasmic reticular systems (SRs). In the contracted state, they were located within the cytoplasm. At the “catch” state, they were found in both the cytoplasm and at peripheries, although the number of precipitates in peripheral areas was small. Thus, we show that calcium translocates in the cells during resting-contraction-catch cycles of “catch” muscle contraction.

Fine structure, Histochemistry, and Morphogenesis During Excystment of the Podocysts of the Giant Jellyfish Nemopilema nomurai (Scyphozoa, Rhizostomeae)

Production of podocysts is the exclusive form of asexual reproduction by polyps of the giant jellyfish Nemopilema nomurai, which has been recurrently blooming in the East Asian seas in the last decade. Podocycts consist of a dome-shaped chitinous capsule with laminated structure that encapsulates a mass of cyst cells filled with granules containing nutrient reserves such as proteins, carbohydrates, and lipids. Mitochondria, rough endoplasmic reticulum, and Golgi complexes are scarce in the cytoplasm of these cells, and the staining reaction for RNA is weak, indicating very low metabolic activity. Podocysts are capable of dormancy for at least 5 years without significant change of internal structure or nutrient reserves. Integrated information about spontaneous and artificially induced metamorphosis suggests that the following processes occur during excystment: (1) nematocyst formation in the internal cell mass, (2) stratification of the cell mass into endoderm and ectoderm, (3) extrusion of the cell mass through a gradual opening of the capsule, (4) formation of primordial polyp mouth and tentacles, and (5) metamorphosis to a polyp. We morphologically confirmed that N. nomurai podocysts have the capacity for long-term dormancy, an ability that should contribute to the periodic nature of the massive blooms of medusae of this species.

Structural changes of gonads during artificially induced gametogenesis and spawning in the giant jellyfish Nemopilema nomurai (Scyphozoa: Rhizostomeae)

We conducted a histological investigation of the ovaries and testes during the gametogenesis and spawning in the giant jellyfish Nemopilema nomurai, which has bloomed in East Asian marginal seas almost annually since 2002 . Oocytes arising from the ovarian epithelium make intimate contact with special epithelial cells, called trophocytes, which have microvilli on the subgenital sinus side, Golgi complexes and vesicles in the cytoplasm. In the early vitellogenic stage, yolk bodies occur in the ooplasm adjacent to the trophocytes, suggesting that the trophocytes transfer nutrients from the subgenital sinus to the oocyte. Later, yolk bodies are formed by the Golgi complexes in the entire ooplasm and accumulate until the oocyte matures. In the late vitellogenic stage, the oocyte separates from the trophocytes and forms microvilli on its surface, indicating nutrient uptake from the surrounding mesoglea. Nutrient support from the trophocytes in the early vitellogenic stage may make the oocytes mature rapidly after medusae are physically damaged. Microvilli-rich epithelial cells also associate with sperm follicles where spermatocytes arise from the follicle cells and accumulate, but their function in nutrient uptake is possibly less than that of trophocytes according to their morphology. During ovulation, which takes 1 . 5 hours after light exposure, trophocytes separate from each other and make an ovulation pit where the oocyte passes out to the subgenital sinus with the surrounding basal lamina. Spermiation occurs 5-20 minutes after light exposure, and spermatozoa are liberated through the spermiation pit that was formed by which the microvilli-rich cells dissociate. The trophocytes in ovaries and microvilli-rich cells in testes have important roles not only in the gametogenesis but also in the spawning of N. nomurai.

Localization of a visual Gq protein in the photoreceptors of a polychaete, Perinereis brevicirris (Annelida)

Abstract Heterotrimeric GTP-binding proteins (G proteins) play an important role in phototransduction. The presence of G-protein subclasses has been reported in photoreceptive membranes, e.g., the Gi subgroup (transducin) in vertebrate rods, and the Gq subgroup in the eyes of the Arthropoda and the Mollusca. We examined the immunoreactivity and distribution of a Gq homologue in the cerebral ocelli of Perinereis brevicirris (Polychaeta, Annelida) using an anti-GqC antibody raised against a conserved sequence at the C-terminal of the α-subunit of Gq (Gq-α). The anti-GqC antibody labeled a 48-kDa band on the Western blot of proteins from the Perinereis ocelli. The anti-GtC antibody, which is raised against the C-terminal sequence of bovine transducin α-subunit (Gt-α), did not cross-react to the ocellar proteins of Perinereis. The rhabdomeric layers of the anterior and posterior ocelli were strongly labeled by anti-GqC on light-microscopic immunohistology. Immunoelectron microscopy showed that the Gq molecules were specifically localized in the photoreceptive membrane of the rhabdomeric microvilli. These results suggest that the Gq protein plays a role in the phototransduction of the Perinereis ocelli.

Anomalous Infrared Taxis of an Aquatic Animal, the Giant Jellyfish Nemopilema nomurai (Scyphozoa, Rhizostomeae)

Remote sensing of thermal radiation (infrared wavelengths) has been reported only in some terrestrial animals and is known to have significant physiological and ecological meaning. In aquatic animals, however, it has not even been discussed because water almost completely absorbs infrared (IR) wavelengths, and such sensitivity has been regarded as useless in aquatic environments. Here we report, for the first time, an anomalous behavior—swimming toward an IR-radiating source—in an aquatic animal, the giant jellyfish, Nemopilema nomurai. Experiments were performed with laboratory-reared juvenile medusae of Nemopilema in a small experimental chamber. In all 52 trials, the majority (average: 78.3%; variation: 63.3%– 94.3%) of the medusae gathered on the IR-irradiated half of the chamber. Near-IR (850/940 nm) and visible light neither attracted the medusae nor induced taxis. A series of results indicated that the juveniles of Nemopilema tended to flock toward a mass of warmer water. Although the exact physiological and ecological meaning of this behavior is uncertain, it might be possible to consider infrared taxis as one of the behaviors in marine ecosystems. It may thus be useful to re-examine the swarming behavior reported in some jellyfish species from the viewpoint of IR taxis. Infrared (IR) sensitivity is known to be mediated by the so-called pit organs, which enable crotaline and boid snakes to apprehend homeothermic prey (1–7) and vampire bats to detect IR radiation from blood-rich locations (8, 9). Moreover, similar mechanisms have been reported in some insects such as fine debris species of beetle (10–13), bloodsucking bugs (14), and some butterflies (15, 16). In aquatic animals, however, little is known about the IR sensitivity. This is the first report to describe an anomalous IR-tactic behavior in the giant jellyfish, Nemopilema nomurai, living in an aquatic environment. Nemopilema nomurai Kishinouye 1922 is one of the largest scyphozoan jellyfish, measuring 1–2 m in diameter and weighing 100–200 kg. Massive blooms of this species have occurred almost annually since 2002, severely affecting coastal fisheries in the Sea of Japan. The life cycle of N. nomurai has been well established by us and our coworkers (17, 18), so the juvenile medusae are easily available. We thus used laboratory-reared juveniles (extended bell diameter, 8–15 mm) to examine the IR sensitivity of N. nomurai. The experimental chamber (width 30 cm, length 24 cm, height 16 cm) used to test IR sensitivity was made from transparent acryl resin plate (5 mm thick). It was filled with seawater to a depth of 3.5 cm and 20 to 35 juvenile individuals were added. The distribution of the medusae in the chamber was monitored by photographing them from above with a photographic strobe every 30 or 60 min. The IR wavelengths were obtained from a tungsten-filament lamp (40 W) by passing the light through a long-pass filter (50% cut-on at 990 nm; LIO-990, Asahi Spectra Co. Ltd.). The tungsten-filament lamp was fixed in a lightproof aluminum housing with a window, where the long-pass filter was mounted. All possible heat sources, except for the IR-wavelength source, were excluded from around the experimental chamber. Near-IR wavelengths, 940 and 850 nm, were obtained from two types of 1.2-W LEDs, LB12WP01 and LC12-WP01 (Ebisu Electronics Co. Ltd.), reReceived 1 August 2011; accepted 20 October 2011. * To whom correspondence should be addressed. E-mail: ohtsu@ life.shimane-u.ac.jp Reference: Biol. Bull. 221: 243–247. (December 2011)

Physiological and ultrastructural studies on glycerinated body wall of sea cucumber

Division of Bioresource Science, The United Graduate School of Agricultural Sciences, Tottori University, Tottori 680-8553, Oki Marine Biological Station, Education and Research Center, Faculty of Life and Environmental Science, Shimane University, Oki, Shimane 685-0024, and Department of Biological Science, Faculty of Life and Environmental Science, Shimane University, Matsue, Shimane 690-0823, Japan

The glycerinated body wall of the sea cucumber as a suitable preparation for electron microscopic and physiological studies of ‘catch mechanism’

The body wall of the sea cucumber changes its stiffness by ionic environments. The stiff state can be held for a long time, and the mechanism concerned is known as ‘catch mechanism’. In the present study, the direct effects of ions on the mechanism using the glycerinated body wall treated with 50% glycerin to clarify how the ions effect changes of stiffness were examined. The glycerinated body walls contained collagen fibers and some broken cells in the connective tissue ultrastructurally. Cell membranes were not clearly present in the broken cells, and cell organelles were dispersed around the cells. The glycerinated body walls went into a limp state during addition of 10 mM ethylenediaminetetraacetic acid (EDTA), and showed height elongation rate in this study’s experimental system. In contrast, the elongation rate decreased by the addition of 10 mM CaCl2, that is, the body wall came to a stiff state. This stiff state could be considered as equivalent to ‘catch state’ of glycerinated body wall. Collagen fibers in those samples showed more compact arrangements at 10 mM CaCl2 treatment than the one of 10 mM EDTA ultrastructurally. These features and physiological results suggested that EDTA and/or CaCl2 from outside affect directly to the main part of the ‘catch’ mechanism in the glycerinated body wall.

Ultrastructure and localization of a visual Gq protein in ied epitoke ocelli of Perinereis brevicirris (Polychaeta, Annelida)

Functional ultrastructural changes in the rhabdomeric photoreceptors of the cerebral ocelli are described for normal and sexually mature (epitoke) Perinereis brevicirris (Polychaeta, Annelida). With sexual maturation, the cerebral ocelli hypertrophied, increasing in volume to 5.5 times that of ocelli in the normal state, and the thickness of the retinal layer increased up to 10 times. Perinereis ocelli have a pigmented retinal layer consisting of at least two cell types: photoreceptor cell (PR) and pigmented supporting cells (PS). In epitoke ocelli, PR bear well-developed rhabdomeric microvilli, multilamellar bodies, and numerous cytoplasmic membranous structures, including vesicles, smooth endoplasmic reticulum, and secondary lysosomes. Localization of a visual Gq protein in the ocelli was studied with anti-GqC antibody. The antibody strongly labeled not only microvilli and multilamellar bodies throughout the retinal layer, but also secondary lysosomes and vesicles in the cytoplasm of the PR in the epitoke ocelli, although labeling was observed only in the microvilli and multilamellar bodies in normal ocelli. Reverse transcription/polymerase chain reaction analysis revealed that the amount of G protein α subunit mRNA in the epitoke head increased by roughly twice that of the normal head. Since Gq protein is essential for phototransduction in Perinereis ocelli, these results suggest that the sites are involved in photoreceptive membrane turnover, which occurs much more extensively in epitoke ocelli. Thus, epitoke ocelli may represent a model system for studying rhabdomeric photoreceptive membrane turnover.